Researches and developments have been carried on extensively in order to reduce the feature sizes of transistors for large-scale integrated circuits (LSIs) or thin-film transistors (TFTs) for flat-panel displays. In a silicon semiconductor process, fine line patterning with a design rule of 0.1 μm or less is realized by shortening the wavelength of an exposing radiation source for use in a photolithographic process. However, according to the conventional photolithography technology, the feature size cannot be reduced unlimitedly. Also, as the feature size has been reduced, the costs of exposure systems and masking members have been rising steeply.
Meanwhile, carbon nanotubes (see Non-Patent Document No. 1) and nanowires made of a material with semiconductor type properties (see Patent Document No. 1) have attracted a lot of attention recently. Carbon nanotubes and nanowires are very small structures with a diameter of about 1 nm to about 100 nm and can be formed in a self-organizing manner. That is why with those carbon nanotubes or nanowires, a high-performance electronic device of a nanometer scale could be realized even without adopting those advanced photolithography or etching technologies. For that reason, those nanostructures are expected to contribute to manufacturing high-performance devices at a reduced cost without resorting to those complicated process technologies.
Hereinafter, a conventional method of growing nanowires will be described with reference to FIGS. 18(a) through 18(c). According to the process shown in FIGS. 18(a) through 18(c), nanowires 1004 made of a first material and nanowires 1005 made of a second material are grown in the growing axis direction. In this case, the first and second materials could be either mutually different materials or the same material including the same dopant in two different concentrations. Those nanowires can be grown by known vapor-liquid-solid phase (VLS) growth mechanism.
According to the conventional growing method, first, as shown in FIG. 18(a), catalyst particles 1001 are put on an arbitrary substrate 1002. The catalyst particles 1001 may be arranged by coating the substrate 1002 with a metal colloid solution by spin coating process or by depositing a metal thin film by sputtering process or evaporation process and then atomizing it into particles, for example.
Next, the substrate 1002 with those catalyst particles 1001 is loaded into the growth chamber of a CVD system, for example. As shown in FIG. 18(b), a source gas 1003, including a constituent element of the nanowires, is introduced into the chamber and maintained at predetermined temperature and pressure. In such an environment, the source gas 1003 selectively decomposes only in the vicinity of the catalyst particles 1001. Meanwhile, the catalyst particles 1001 react to this decomposed source gas, thereby making an alloy of the catalyst particles and the constituent element of the nanowires. The constituent element of the nanowires, which has been produced as a result of the decomposition of the source gas 1003, dissolves in the alloy of the catalyst particles and the constituent element of the nanowire to get the alloy supersaturated. Then, the constituent element of the nanowires precipitates out of the supersaturated alloy and then coagulates together, thereby growing a first type of nanowires 1004 made of the first material. By maintaining such a state for a predetermined amount of time, the nanowires can be grown to any desired length.
Next, as shown in FIG. 18(c), a second type of nanowires 1005 of the second material can be grown by changing the gases to introduce into the growth chamber.
As can be seen, according to the nanowire growing technology, the in-situ doping or hetero-epitaxy could be controlled on a nanometer scale as in a normal thin-film epitaxy process. Also, since the nanowires have a pseudo one-dimensional structure, the stress that has been caused due to a lattice constant misfit in the conventional thin-film deposition technology could be relaxed. Thus, it is expected that restrictions on the selection of materials would be removed by adopting such a technology.
Thus, nanowires that would contribute to forming a very small structure in a self-organizing manner or developing material engineering are one of the most prospective nanostructures.                Patent Document No. 1: PCT International Application Japanese National Phase Publication No. 2004-535066Non-Patent Document No. 1: R. Martel, et. al., “Single- and Multi-wall Carbon Nanotube Field-Effect Transistors”, Appl. Phys. Lett. 73, pp. 2447, 1998Non-Patent Document No. 2: E. Tutuc, et al., “Doping of Germanium Nanowires Grown in Presence of PH3”, Appl. Phys. Lett. 89, pp. 263101, 2006        